>
>measures wrote:
>>>
>>>Did you actually mean to say VLF parasitics?
>>>
>>? Just how this is possible is somewhat less than obvious.
>
>VLF resonances are *the* main cause of parasitic oscillation in VHF/UHF
>power amps.
[chortle]
>They generally arise because half-wave tuned lines become
>open-circuits at low frequencies, so that both the input and output of
>the tube are unloaded. There are then possibilities for oscillation due
>to unwanted resonances between RF bypass capacitors and lead inductances
>or RFCs in the power supply and bias circuits. Another useful function
>of the "glitch resistor" is to damp any such resonances in the B+
>circuit.
>
>Returning to the SB-220 and similar amps, what is the parallel resonant
>frequency of the grid bypass cap and the RFC? Whatever it is, the grid
>is totally ungrounded to RF at that frequency.
>
In the Rauchian world of alleged VLF oscillations, one ignores the
reactance of C-anode/cathode at VLF.
end
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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